The invention relates, generally, to an automated machine for applying evaporator beads to a conductive wire.
Evaporator beads typically consist of antimony, manganese or other metals formed on metal wires. For example, where the bead is formed of antimony the wire is platinum coated molybdenum and where the bead is manganese the wire is tungsten. Other metals for the bead and wire can be used as desired. An example of such evaporator beads is shown in U.S. Pat. No. 4,357,368 to Longsdorff et al. To use the evaporator beads, the wire carrying the beads is located closely adjacent to a substrate to be coated. For example, the wire can extend through a photocathode. An electrical current is passed through the wire thereby heating the wire and vaporizing the evaporator bead. The vapor generated by the evaporating bead is deposited on a surface such as glass to create a layer or coating thereon.
While the use of such evaporator beads has proven to be an excellent method for coating surfaces such as photomultiplier cathodes, semiconductor surfaces and optical mirrors, the existing methods for forming the evaporator beads on the wire are inefficient. Presently, preformed beads, manufactured by processes such as that shown in Longsdorff et al., are applied to the wire by hand. This process is relatively slow and labor intensive. As a result, evaporator bead wire is extremely expensive. Moreover, the manual process results in significant waste of wire and bead material. And, the beads formed on the wire are not uniform in size and shape.
Thus, an automated method and apparatus for forming evaporator beads on conductive wire cheaply and efficiently is desired.